The ploy isn't new -- security experts have seen it in circulation for at least a year -- but Microsoft was the first to quantify the problem.

According to Microsoft, which sponsored surveys in the U.S., the U.K., Ireland and Canada, 15% of the people polled said they had received unsolicited calls from fraudsters posing as computer support technicians who claimed they were offering PC security checks.

The scammers try to trick users into believing that their computer is infected -- often by having them look at a Windows log that typically shows scores of harmless or low-level errors -- then convince them to download software or let the "technician" remotely access the PC.

The con artists charge for their "help" and often get people to pay for worthless software. In actuality, the software is malware that steals online account information and passwords.

"They're taking advantage of ignorance," said Sean Richmond, a senior technology consultant for Sophos, in a today.